This invention relates to a technique for multi-layer fabrication of components for an electrochemical apparatus. More particularly it relates to a method for producing fine features on components for an electrochemical apparatus. In a preferred embodiment, it relates to a method of creating component features made of electrochemically active material by using radiation curable polymers combined with electrochemically active materials applied by printing in a specified pattern.
Attempts have been previously made to provide for reproducibility of electrochemical device component materials, to decrease the expense in production methods, to use less high cost materials, to lower the overall cost of the component, and, in the case of gas permeable electrodes, to decrease the back pressure of the electrode material by using thinner layers with higher porosity. A feasible method of accomplishing these goals has not yet been achieved.
Methods of fabrication that have been used for components in electrochemical device such as fuel cells, electrolyzers, electrochemical transport reactors and others include a variety of conventional techniques such as photolithography, pressing, calendering, deposition techniques, or printing. Features in individual components may be induced in the components by electrical-discharge machining, stamping, laser ablation, chemical etching, ultrasonic etching, scribing, and grinding.
As an example of a well developed electrochemical apparatus, fuel cells offer many advantages over conventional power generation systems. It is generally known that such devices are capable of delivering high quality electric power with greater efficiency and lower emissions when compared to comparably sized gas or diesel fed generators. Further, because such systems are generally modular they can serve a wide range of power demands from remote site power generation, central utility, and transportation applications as well as commercial and residential applications. A type of fuel cell to which this invention is applicable is the solid oxide electrolyte fuel cell (SOFC).
In traditional SOFCs, air brushing or ink printing of layered structures requires either long drying times or a separate piece of equipment such as a heated drying oven. Attempts to apply additional layers on uncured layers leads to very poor layer definition (e.g., blurring, bleeding, sagging) and yield generally unsatisfactory results.
By contrast, photon-catalyzed binder systems often cure within seconds. Exposure to certain frequencies of radiation creates activated carbon centers (carbon radicals) on the binder system""s polymer chain that initiate the cross linking and causes the polymer to harden. Frequently, organic compounds that are sensitive to particular radiation frequencies are incorporated into the binder system as a second component. These compounds, termed initiators or photo-initiators, are generally selected to be sensitive to radiation frequencies in ranges that are either easy to produce or that are free from interference from other components that may be in suspension in the binder. The preferred photon source for initial evaluation is an ultraviolet laser. Ultraviolet cured polymer systems are well documented and widely used in a number of industries. There are several other types of radiation curable polymers that are known in various fields; electron beam (EB), infra-red (IR), radio frequency, visible light, and microwave cured systems. An alternative method of rapidly curing polymers is by direct chemical initiation, that is, a rapidly catalyzed polymer system.
For multi-layer printing, a well defined registration reference point is also required which is not always practical in solid oxide fuel cell (SOFC) designs. In one cell design, three axial reactant feed holes provide an excellent opportunity for registration and alignment. However, for precise alignment, even these reference points are not always ideal since the substrate is a xe2x80x98net shapexe2x80x99 part and may still exhibit some non-uniformity during sintering.
All planar SOFCs have a conceptually similar method for reactant gas distribution. A manifold system (either internal with seals or external) is used to channel gas on opposing sides of an ionic conducting electrolyte membrane. For certain SOFC designs, the reactants are xe2x80x98channeledxe2x80x99 through grooves that are cut or machined into either a metallic or ceramic bipolar separator plate. Some designers have sought to reduce costs by employing light foil corrugated separators.
One SOFC design uses an alternate method of distribution and instead, distributes the reactants through porous electrode material. This has the advantage of being a net shape part without post processing and facilitates a flat, featureless separator that is conducive to mass production at minimal cost. However, current methods of porous electrode production involve techniques that produce significant waste material (thereby increasing cost) and do not allow for flow complexities that may improve electrochemical performance.
In order to produce a component or feature of a component using a multi-pass printing technique, registration of an array is required. In practice, proper registration of the array is critical in order to ensure uniform height and contact area and has been beyond the existing state of the art. To achieve reliable low cost fabrication, a method of creating electrochemical apparatus component features, such as integral gas distribution manifolds is required.
It is therefore an object of this invention to establish a method of manufacture of electrochemical device components that allows rapid fabrication, in one embodiment, preferably based upon common fabrication methods such as printing.
It is yet another object of the present invention in another embodiment to include easily graded properties including composition, morphology, and geometry into the electrochemical device components without increasing fabrication complexity or cost.
It is yet another object of one embodiment of the present invention to build up thick layers without complicated registration issues.
At least one or more of the foregoing objects, together with the advantages thereof over the knowvn art relating to a method for fabricating components for an electrochemical apparatus, which shall become apparent from the specification that follows, are accomplished by the invention as hereinafter described and claimed.
This invention is a process by which features of components of an electrochemical apparatus can be screen-printed using multi-layer techniques with minimal waste. This single production method simplifies the current production process and decreases the costs for production. In one embodiment, the entire cell (gas distribution manifold, seals, current distribution layers, and primary electrodes) can be produced using this method.
To address the problems in the present SOFC electrode system, we have increased the porosity of the electrode, by applying the low field by printing, using novel polymer systems. These polymer systems use a rapidly cured binder in the printing ink to produce multi-layer components without the need for re-alignment (re-registry between prints). This is a processing change which increases performance and lowers back pressure, engendering the benefits set forth below.
This invention provides a component for an electrochemical apparatus and a process for the fabrication of a component for an electrochemical apparatus including providing a printing medium comprising a rapid curable polymer containing carrier and a powder of a component material precursor; printing one of a uniform layer or a pattern of the printing medium on a substrate, and rapidly curing the curable polymer to form a cured part.
Additionally, the invention provides an electrochemical apparatus and a process for the fabrication of a component feature for an electrochemical apparatus comprising: providing a printing medium which includes a rapid curable polymer, and a powder of a component material precursor, printing a component feature with the printing medium on a substrate, and rapidly curing the curable polymer to form a cured part. The component feature may be one of a uniform layer or a pattern of material.
This invention also provides an electrode for an SOFC and a process for the fabrication of an electrode for an SOFC comprising providing a printing medium comprising a rapid curable polymer containing carrier and a powder of an electrode material precursor, printing one of a uniform layer or a pattern of the printing medium on a substrate, and rapidly curing the curable polymer to form a cured part.
Additionally, this invention provides an SOFC, a component of an SOFC, and a process for the fabrication of a component for a multi-layer cell of an SOFC which includes providing a printing medium comprising a rapid curable polymer containing carrier and a powder of a component material precursor, printing one of a uniform layer or a pattern of the printing medium on a substrate, and rapidly curing the curable polymer to form a cured part.
The invention further provides a multi-layer cell of an SOFC, an SOFC, and a process for the fabrication of a multi-layer cell of an SOFC comprising a) providing a first printing medium comprising a radiation curable polymer containing carrier and a powder of a first component material precursor; b) printing one of a uniform layer or a pattern of the first printing medium on a substrate; c) radiation curing the curable polymer to form a cured part, and; repeating steps a), b), and c) with at least a second printing medium containing a powder of a component material precursor of at least one subsequent component.
In certain embodiments, the rapid curable polymer is a radiation curable polymer, and cure of the polymer during fabrication is by radiation curing. The radiation cure can be by any of the following means: ultraviolet, infrared, electron beam, radio frequency, visible light and microwave, and techniques for their use are well knowvn in the art. Where radiation curing is by ultra-violet, infrared or visible light, the printing medium may include a radiation curable polymer, a carrier, and a photo-initiator. An alternative method of rapidly curing of polymers is by direct chemical initiation, that is, a rapidly catalyzed polymer system. A chemical initiator can be sprayed concurrently with or alternatively onto, the rapidly curable polymer.
The invention also provides for heat treating the cured part to form the component.